Process for making a panel with a protected acoustic damping layer and acoustic panel as made

ABSTRACT

A process for the production of a panel with a protective acoustic damping layer. The protective layer includes at least one porous core covered, on the one side, with a porous acoustic damping layer and on the other side with an acoustic reflector. The porous damping layer is emplaced by striping or draping. The porous damping layer consists of parallel strips. Edges of the strips of the porous damping layer are positioned facing a strip deposited by striping or draping and containing a thermoplastic, thermosetting or thermofusible material adapted, by subsequent heating, to ensure the securement of the edges of said strips of the porous damping layer with the adjacent strip of thermoplastic, thermosetting or thermofusible material.

BACKGROUND OF THE INVENTION

The present invention relates to panels with acoustic attenuation andmore particularly to those lining the annular fan channels formed in thenacelles of turbo motors, particularly of aircraft.

Such panels form the envelope, on the fan channel side, of the nacelle,behind the air inlet lip and have a structure adapted to attenuate thenoise produced by the central portion of the motor surrounded by thenacelle and particularly the noise produced by the fan.

In practice, these panels include a porous core such as a honeycombstructure covered, on the fan channel side, with an acoustic dampinglayer and, on the opposite side, a rear reflector.

The acoustic damping layer is a porous structure with the role ofdissipating, which is to say partially transforming, the acoustic energyof the sound wave passing through it, into heat.

This porous structure can be, for example, a metallic cloth or a clothof carbon fibers whose weave permits fulfilling its dissipatingfunction.

These acoustic panels must also have sufficient structural propertiesparticularly to receive and transfer aerodynamic and inertial forces andforces connected with supporting the nacelle, toward the nacelle/motorstructural connections, and so it is necessary to impart structuralproperties to the acoustic damping layer.

To this end, there can, as shown in British patent 2 130 963, provide anacoustic damping layer with two components, namely a structural layer,on the honeycomb side and a porous surface layer, or else use as thedamping layer a cloth combining both the acoustic function and thestructural function by selecting a diameter of the filaments of thecloth giving to this latter a high resistance to forces coupled withgood acoustic damping.

For making such panels, there is known the process consisting inproducing the annular assembly forming the wall of the fan channel intwo interfitting half channels comprising, for each half panel, thefollowing steps:

predeforming a layer of porous structure on a form identical to a halfpanel, with the help of jaws stretching the porous material to itselastic limit,

acoustically measuring the shape thus produced so as to qualify the meanvalue of the acoustic porosity,

adapting to the mean value above, the spacing of winding of the carbonfilaments adapted to be deposited on the porous layer to constitute astructural layer,

emplacing on a suitable mold the predeformed shape,

then making the half panel by known techniques of winding said carbonfibers, and emplacing the porous core and the rear reflector.

This process has drawbacks.

Thus, the shape to be produced not being a figure of revolution, thereexists in the deformed layer inhomogeneous regions, which is to sayregions stretched and regions stressed, which degrade the generalacoustic quality of the porous structure. The interval of winding thecarbon fibers being adapted to the mean value of acoustic porosity ofthe structure, the inhomogeneous regions introduce variations in theacoustic attenuation of the noise generated by the motor.

Moreover, the presence of interfitting connections of the two halfpanels introduces two regions of acoustic refraction in the finalacoustic panel, which is prejudicial to the quality of damping thenoises generated by the motor.

To overcome these drawbacks, there can, as taught by French patent 2 767411 in the name of the applicant, be emplaced an acoustic damping layerby winding with a porous material present in the form of strip.

This manner of proceeding not only permits avoiding inhomogeneousregions of the porous layer from an acoustical standpoint, as indicatedabove, in the conventional manner of fabricating the two half panels,but also eliminates the necessity of interfitting, the winding of theporous layer being adapted to form other layers, namely the structurallayer, the porous central core, the rear reflector, so as to produce acomplete acoustic panel in a single piece, without interfitting.

The absence of interfitting permits increasing the effective acousticsurface of the panel, of decreasing its weight and reducing the time andcost of production.

However, an acoustic panel of such a structure uses constituent stripsof the porous layer in direct contact with the flow of aerodynamic fluidin the fan channel. When these strips are made of metallic cloth, theyare easily peeled back at their edge in contact with the aerodynamicflow, the more so as they are disposed substantially perpendicular tothe direction of said flow.

Thus, not only the acoustic qualities of the panel are degraded, butmoreover, the panel itself is degraded and must be changed, which givesrise to maintenance and down time costs of the aircraft.

The present invention has for its object to overcome these drawbacks byimproving the winding technique described in FR 2 767 411.

SUMMARY OF THE INVENTION

To this end, the invention has for its object a process for theproduction of a panel with a protected acoustic damping layer,comprising at least one central core with a porous structure covered, onthe one hand, with a porous acoustic damping layer and, on the otherhand, a totally acoustic reflector, in which at least said porous layeris emplaced by winding or draping, said porous layer being constitutedby parallel strips, characterized in that the edges of the strips of theporous layer are positioned facing a strip deposited by winding ordraping and containing a thermoplastic, thermohardenable orthermofusible material adapted, by ultimate heating, to ensure thesoliderization of the edges of said strips with the adjacent strip.

According to a way of proceeding adapted more particularly to theproduction of a panel in a single piece, without interlocking, ofgenerally annular shape, the porous layer and said strip containing athermoplastic, thermohardening or thermosfusible material, are wound ordraped on a mold having the shape of the panel to be produced, theporous structure and the total reflector being then emplaced also bywinding or draping.

Other panels, convex or concave, or non-annular, can be producedaccording to the process of the invention and preferably simultaneouslyfrom a same mold on which are wound or draped the various layersconstituting the panels.

According to the order of laying down the different layers on the mold,there will be obtained a panel with a concave or convex porous layer.

There can thus be produced for example panels constituting pressurereversing doors or panels with interconnections for a nacelle.

According to one embodiment of the process, said strip containing athermoplastic, thermohardening or thermofusible material is constitutedof filaments pre-impregnated with a thermohardening or thermoplasticresin, said strip constituting a structural layer associated with theporous acoustic layer and adapted, which is the case for use of theprocess of the invention for the production of air inlet acoustic panelsfor a nacelle, to transfer the dynamic and inertial forces as well asthose connected with the support of the nacelle, toward the structuralconnections.

By filaments, there is meant an assembly of square, round or rectangularcross-section filaments, of strips of filaments, of meshes, of bundlesor layers of filaments, of different nature, for example of carbon,glass or “Kevlar”.

These filaments in the general sense defined above are deposited forexample by winding in various ways and are used essentially in the caseof a non-joined deposition of the windings of the porous acousticdamping strip, by covering the intervals between windings.

According to a first embodiment, said filaments are wound on the porouslayer, so as to be sandwiched between this latter and the porous core,subsequently deposited, for example by winding of a honeycomb structurein the form of a strip.

The windings of the filaments are spaced from each other and only facingand overlapping the intervals between the strips of the porous layer.

According to another embodiment, said filaments are wound first on themold so as to be located at least facing and overlapping the intervalsbetween the strips of the porous layer which is wound subsequently andwhich will therefore be located as a sandwich between the structurallayer formed by the filaments and the porous structure, identical forexample to the preceding case.

Here again, the filaments are separated from each other and are not anobstacle to the accomplishment by the porous subjacent layer, of itsdissipating function.

According to still another embodiment which is a compromise between thetwo preceding ones, said filaments are disposed on opposite sides of theporous layer but always so as to cover at least the intervals betweenstrips of said porous layer.

According to a second embodiment of the process, said strip containing athermoplastic, thermohardening or thermofusible material is a strip ofperforated metal sheet clad with a film of glue and used for examplewith a porous layer constituted as in the example of the firstembodiment of the process.

These strips of perforated metal sheet are deposited by windingaccording to various manners.

According to a first manner, the strips of perforated metal have a widthequal to or less than that of the strips of the porous layer and aredisposed in the first instance on the mold with an interval between twosuccessive strips, then the porous layer is deposited in strips facingsaid intervals between strips of sheet metal.

According to a second embodiment, the strips of perforated metal have awidth substantially greater than that of the strips of the porous layerand are disposed in the first instance on the mold with a slight partialoverlapping between strips, then the porous layer is deposited such asfor example to align each porous strip with a strip of sheet metal, thewindings of the porous layer not touching each other.

According to a third embodiment, the strips of perforated metal have awidth less than that of the strips of the porous layer, which is firstdeposited on the mold, such that the windings slightly overlap, then thestrips of metal are disposed facing or not the regions of overlap of thestrips of the porous layer, these strips not touching each other.

According to a third embodiment of the process, said strip containing athermoplastic, thermohardening or thermofusible material is constitutedin fact by the porous layer itself, which is formed from a cloth offilaments pre-impregnated with a thermohardening or thermoplastic resin.The filaments are thus selected with a diameter giving to the cloth orthe like thus constituted, a high resistance to force coupled with agood acoustic dampening, the porous layer forming at the same time astructural layer.

In this third embodiment of the process, the single layer is wound onthe mold so as to form strips or windings with a slight mutual overlap.

In all the examples given above, there are obtained panels whichacoustic damping layer, which is necessarily turned toward theaerodynamic flow, is protected at the edges of the strips constitutingsaid layer, because these edges are firmly secured on the one hand to asublayer or an overlayer, according to the method of application, with aconnection of the constituents of the layers by means of a suitableresin or glue.

Any peeling of the edges of the strips forming the acoustic dampinglayer by the aerodynamic flow is thus prevented and the mechanicalproperties as well as the strength over time of the panels, aresubstantially reinforced.

The invention also of course has for its object the acoustic dampingpanels obtained according to the above process, no matter what thecontext in which they are used.

BRIEF DESCRIPTION OF THE DRAWINGS

There will now be described in greater detail the embodiments mentionedabove referring to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of an aircraft motor;

FIG. 2 is a fragmentary axial cross-section of the nose of the motor ofFIG. 1;

FIG. 3 is a fragmentary cross-sectional schematic view of an acousticdamping panel of the type used in the nacelle of the motor of FIG. 1,the cross-section being along the axis of the fan channel;

FIG. 4 shows schematically a first embodiment of the process of theinvention;

FIG. 5 is a cross-section along the axis of air flow, of the acousticdamping layer of a panel according to the embodiment of FIG. 4;

FIG. 6 shows schematically a second embodiment of the process;

FIG. 7 is a cross-sectional view analogous to that of FIG. 5, andrelative to the acoustic layer of a panel according to FIG. 6;

FIG. 8 shows schematically a third embodiment of the process;

FIG. 9 is a cross-sectional view analogous to that of FIG. 5 andrelating to the acoustic layer of a panel according to FIG. 8;

FIG. 10 shows schematically a fourth embodiment of the process;

FIG. 11 is a cross-sectional view analogous to that of FIG. 5 andconcerning the acoustic layer of a panel according to FIG. 10;

FIG. 12 shows schematically a fifth embodiment of the process;

FIG. 13 is a cross-sectional view analogous to that of FIG. 5 andrelating to the acoustic layer of a panel according to FIG. 12;

FIG. 14 shows schematically a sixth embodiment of the process;

FIG. 15 is a cross-sectional view analogous to that of FIG. 5 andrelating to the acoustic layer of a panel according to FIG. 14;

FIG. 16 shows schematically a seventh embodiment of the process;

FIG. 17 is a cross-sectional view analogous to that of FIG. 5 andrelating to the acoustic layer of a panel according to FIG. 16;

FIG. 18 shows schematically an eighth embodiment of the process, and

FIG. 19 is a cross-sectional view analogous to that of FIG. 5 andrelating to the acoustic layer of a panel according to FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There is shown in FIG. 1 an aircraft turbo reactor comprising a nacelle1 coaxially surrounding the motor properly so-called and fixed forexample to a wing (not shown) of the aircraft by means of a mastdesignated generally by reference numeral 2.

The nacelle 1 has an annular cross-section and defines between itselfand the central portion of the motor, an annular so-called fan channel3. There is shown at 4 in the figure the nose in the form of a roundedcone of the fan driven by the motor and which is disposed at the inletof the channel.

The front portion 5 of the nacelle 1 constitutes an air inlet structurewhich has particularly the function to ensure the aerodynamic flow ofthe air, on the one hand, toward the fan channel 3 and, on the otherhand, toward the outside of the nacelle 1.

As can be seen in FIG. 2, which is an axial cross-section of the nose ofthe nacelle 1, the air inlet structure is comprised conventionally of anair inlet lip 6 having a rearwardly opening U-shaped cross-section. Thislip forms the external envelope of the front portion of the air inletstructure and ensures the division of the air between the portion 7which enters the fan channel 3 and the portion which flows about thenacelle.

The air inlet structure comprises, in addition to the lip 6, a frontreinforcing frame 8 and an acoustic attenuation panel 9.

This panel 9 has a generally annular shape and defines said fan channelwith its internal surface 10 in contact with the aerodynamic flow 7. Thepanel has a structure adapted to attenuate noises produced by thecentral portion of the motor and particularly by the fan.

In practice, this structure is conventionally of the composite sandwichtype and comprises, in addition to a porous acoustic damping layerconstituting the surface 10, a porous core 11 such as a honeycomb and,opposite the porous layer 10, a layer 12 forming a total acousticreflector.

The porous structure 11 can be simple, which is to say a singleresonator or a multi-layer or even multiple porous core, which is to saywith superposed resonators or with a porous core formed of severalsuperposed layers separated or not by septa.

The process of the invention is applicable particularly to theproduction of acoustic damping panels such as the panel 9.

FIG. 3 shows the structure of a panel of this type made according to theteaching of FR 2 767 411 and constituted by a monobloc panel withoutjoints and of a generally annular shape, comprising a central annularcore comprising a porous central core 11, for example a honeycomb,covered, on the side of air flow 7, with an acoustic damping layer 10deposited on winding or draping and, on the opposite side, a rearreflecting layer 12.

The acoustically resistive layer 10 is made for example from a porousstructure available in strips and which is emplaced by winding helicallyon a mold (not shown) to the shapes and dimensions corresponding tothose of the panel 9 to be produced.

The layer 10 is thus constituted of windings or successive strips 13separated by a constant interval 14 and whose edges, particularly theattack edges 15, which is to say those exposed in the first instance tothe aerodynamic flow 7, are substantially perpendicular to the axis offlow. This renders them fragile and risks giving rise to peeling of thestrips 13 under the effect of the flow 7.

The invention seeks precisely to overcome these drawbacks.

According to a first embodiment of the process of the invention shown inFIGS. 4 and 5, after emplacement by winding on a mold indicated at M inFIG. 5, in appropriate shapes and sizes, the successive strips 13 spacedfrom each other by an interval 14 constituting the acoustic dampinglayer 10 of the panel, there is emplaced, also by winding, in line withthe intervals 14, filaments forming narrow bands 16 by covering andslightly extending beyond said intervals 14.

These strips 16 thus cover the facing edges, hence the so-called attackedges 15, of the strips 13 of porous structure.

The damping layer 10 is for example a cloth formed by stainless steelgrid or a cloth of carbon fibers or glass fibers pre-impregnated with anepoxy or thermoplastic resin.

By filaments constituting the strips 16, there is meant generallyspeaking an assembly of square, round or rectangular cross-section offilaments, strips of filaments, meshes, bundles or strands of filaments.These filaments can be of different types, such as carbon filaments,glass filaments or “Kevlar”, coated with a suitable binder.

These filaments 16 are capable of transforming the dynamic and inertialforces, as well as those connected with the holding of the nacelle,toward the nacelle/motor structural connections.

The porous core (not shown), such as a honeycomb structure, is thenemplaced from above the assembly 10-16, for example also by winding, thesame as the final layer forming the reflector (not shown).

There is thus obtained an acoustic panel whose surface exposed to theaerodynamic flow 7 is formed from a layer with a double function:acoustic damping by the porous layer 10, and structural reinforcement bythe strips of filaments 16.

The dissipating function of the layer 10 can take place in spite of thepresence of filaments 16 which nevertheless leave, on the one hand, alarge portion of the surface of the strips 13 free, which is to sayuncovered, as can be seen in FIG. 5.

It is to be noted that in the region 17 of an edge of the band 13subject to peeling because of the flow 7, any tearing off is preventedby the fact that this edge is secured to a portion of the sublayer (16)facing it, thanks to the resin of the filaments and if desired to theweave of the layer 10, which, by an ultimate thermal treatment, willdiffuse and cover said edge, thereby ensuring the desired protection.

When all the elements of the panel are in place, the panel is unmoldedby disassembly, retraction or melting of the mold on which have beenwrapped the different elements. The consolidation of the edges of thestrips 13 by heating is carried out preferably before demolding.

FIGS. 6 and 7 show a modified embodiment according to which thefilaments 16 in the broad sense defined above, are emplaced on the otherside of the porous strips 13, which is to say on the side of theaerodynamic flow 7, the filaments 16 being for this reason laid downfirst on the mold.

The filaments 16 are disposed as in FIG. 5, astride the intervals 14between strips 13 and furthermore the supplemental filaments 16′ aredisposed substantially in the central region of the strips 13. Thisreinforces the structural function of the filaments 16 whilstnevertheless permitting the strips 13, in their portions uncovered bythe filaments 16, to play their acoustic dissipation role.

FIGS. 8 and 9 show another modification according to which the filaments16 are emplaced alternately on opposite sides of the layer 10.

In these two modifications, there is obtained at 17 the same securementbetween the edges of the strips 13 and the portion of the sublayer oroverlayer (16) facing it, thanks to the resin of the layer or layers inquestion, which will be subsequently heated.

In the case of FIGS. 8 and 9, the double acoustic/structural layer (10,16) is made in three passes, namely a first application of filaments 16,an application of the layer 10, then a second application of filaments16.

FIGS. 10 and 11 show another modification according to which the strips13 of the dissipating layer 10 are substantially wider than thefilaments 16 of the preceding examples. The filaments 16 are disposed onopposite sides of the layer 10, but the covering of the intervals 14 isensured only by the filaments 16 deposited on the flow side 7, thefilaments 16″ on the other side serving only for structuralreinforcement and covering only a portion of the strips 13.

The securement at 17 to the edges of the strips 13 is done as in thecase of FIGS. 6 and 7.

The emplacement of the strips 13, 16, 16″ takes place according to thesame process as in FIGS. 8 and 9.

FIGS. 12 and 13 show another embodiment in which the acoustic layer 10is analogous to that of the preceding examples, but the filaments (16,16′, 16″) are replaced by strips 18 of perforated sheet metal fromstructure in the shape of a strip deposited by striping on the mold,before deposition of the porous strips 13.

The strips 18 are helically wound with an interval 19 between them so asto overlap the intervals 14 of the layer 10.

Thus, the layer 10 can play its acoustic role, however the strips 18take part in reinforcing the structure of the panel.

To ensure at 17 the securement between the attack edge (15) of eachstrip 13 with its facing portion of sheet metal 18, there are usedvarious means according to the nature of the layers 10 and 18.

The layer 10 can be a metallic cloth or a cloth of fiberspre-impregnated with an epoxy or thermoplastic resin.

The sheet metal of the strips 18 is a metallic sheet, of aluminum,titanium or other material for example, or sheet metal of compositematerial constituted for example by a cloth of fibers pre-impregnatedwith a thermosetting or thermoplastic resin.

If the two layers (10, 18) are cloths of fibers pre-impregnated withresin, the soliderization such as at 17 of the edges of the strips 13with the facing metal sheets 18 takes place by ultimate heating of theresin as above.

If the sheet 18 is metallic, the securement at 17 will take place eitherwith the help of the resin of the layer 10, of with the help of thislatter and a thermofusible glue previously deposited on said metallicsheet, or with the help of this glue alone if the layer 10 is a metalliccloth.

FIGS. 14 and 15 show a modification of the process according to FIGS. 12and 13, in which the strips of sheet metal 18 are disposed slightlymutually overlapping, thereby ensuring a total covering of the subjacentstrips 13 which themselves have a width substantially less and aredisposed facing the central region of the sheets 18, with a largeinterval 14 between the strips 13 facing the region of overlap of themetal sheets 18.

The acoustic damping layer 10 plays, thanks to the holes of the sheetmetal 18, its acoustic role, however the sheet metal 18 plays itsstructural role and the edges of the strips 13 are, as at 17, perfectlyplastered against the porous core (not shown) thanks to the resin and ifdesired to the glue of the sheet metal 18, heated subsequently as in thepreceding example.

FIGS. 16 and 17 show two modifications of the preceding example,consisting in reversal of the mutual positions of the respective porouslayer 10 and metallic layer 18.

In variation A, the arrangement is identical to that in FIGS. 14 and 15and merely reversed, the strips 13 of porous structure being slightlymutually overlapping, the attack edges 15 not being in contact with theaerodynamic flow 7.

The securement of the parts by covering the strips 13 is ensured only bythe resin of the cloth of the strips, which is ultimately heated.

In modification B, the arrangement is similar to that of modification Aexcept that the sheet metal 18 is wider and is placed astride theregions of overlap of the porous strips 13, thereby reinforcing theregion of the edges of the strips 13.

Finally, FIGS. 18 and 19 show still another embodiment in which theacoustic damping and structural functions are ensured by a single layer(10′) formed of strips 13′ that slightly mutually overlap.

The strips 13′ are disposed by striping with a strip materialconstituted by a cloth formed of strands or filaments of sufficientdiameter to give to the cloth good resistance to forces coupled with ahigh acoustic damping. The cloth is for example constituted by carbonfibers, glass fibers or “Kevlar” fibers, pre-impregnated with athermosetting or thermoplastic resin which will ensure by heating theadherence of the regions of cloth covering the strips 13′, therebyprotecting the attack edges 15 which are themselves covered by theadjacent strip 13′.

In the various embodiments described above, the thicknesses of thelayers of materials used are small, even in the case of partialoverlying of the layers, not giving rise to aerodynamic impediments,causes of aerodynamic turbulence. Thus, the aerodynamic and acoustichomogeneity is complete over all the internal wall of the final annularpanel.

It is to be noted that the structural layer (filaments 16, 16′, 16″;metal sheets 18) can be deposited by draping.

In all cases in which the structural layer is deposited, as the acousticdamping layer, by striping, it is important to synchronize thedepositions of these layers such that the edges of the acoustic layerswill be protected by a strip of structural layer. The adjustableinterval of deposition of the structural layer permits controlling thequantity of open surface of the acoustic damping layer.

Finally, the invention is clearly not limited to the embodiments shownand described above, but on the contrary covers all modifications,particularly as to the nature of the acoustic damping layer, the natureof the structural layer and the manner of emplacement of the filamentsor strips of the structural layer relative to the strips of acousticdamping layer, as well as the order of emplacement of the differentconstitutent layers of the panel.

Thus in the case of non-annular panels, concave or convex, the processof the invention permits simultaneous production of several panels froma same mold on which are striped or draped the various layers, namelythe porous layer such as 10, the structural layer such as 16 associatedwith the porous layer 10, the porous layer 11 and the layer 12 forming atotal reflector, the order of successive deposition of the layers on themold permitting obtaining panels with a concave or convex protectedporous layer according to the envisaged uses. These panels can compriseflat or complex portions. There can thus be produced for example panelsconstituting doors of pressure reversers.

According to a modification, it is also possible to produce a panel intwo stages by beginning to stripe or drape on a mold the total reflector12, then the porous core structure 11, then, in a second stage, andafter baking in an autoclave and withdrawal of the mold, striping ordraping the porous layer 10 and the pre-impregnated filaments 16 on thecore with a porous structure 11 according to the process of theinvention.

Moreover, in the embodiments shown in FIGS. 4 to 11, the structuralstrength of the panel can be increased by depositing, by striping orwinding, filaments 16, 16′, 16″ that are supplementary and form an anglemore than zero with the other filaments 16, 16′, 16″, these supplementalfilaments being disposed on opposite sides or not, of the porous layer10.

What is claimed is:
 1. Process for the production of a panel with aprotected acoustic damping layer, comprising the steps of: emplacing aporous core between a total acoustic reflector and at least a porousacoustic damping layer; emplacing said porous acoustic damping layer bystriping or draping, in order to obtain parallel strips that are distantfrom adjacent ones of said parallel strips; emplacing only astrideintervals between said parallel strips, filaments pre-impregnated with athermosetting or thermoplastic material; and heating said thermosettingor thermoplastic material in order to ensure the securement of edges ofsaid parallel strips with said filaments.
 2. Process according to claim1, for the production of a single piece panel, without a joint, ofgenerally annular shape, wherein said porous layer and said stripcontaining a thermoplastic, thermosetting or thermofusible material, arestriped or draped on a mold having the shape of the panel to beobtained.
 3. Process according to claim 1, wherein said filaments arestriped on said porous layer, so as to be sandwiched between said porouslayer and a porous core which is subsequently deposited by striping ahoneycomb structure in the form of a strip.
 4. Process according toclaim 3, wherein windings of the filaments are separated from each otherand only facing and overlapping intervals between the parallel strips ofthe porous layer.
 5. Process according to claim 1, wherein saidfilaments are first emplaced by striping on a mold and are located atleast facing and overlapping intervals between the parallel strips ofthe porous layer which are subsequently emplaced by striping.
 6. Processaccording to claim 1, wherein said filaments are disposed on oppositesides of the porous layer so as to at least cover intervals between theparallel strips of said porous layer.
 7. Process according to claim 1,wherein filaments are in the form of an assembly of square, round orrectangular cross-section comprised of filaments, strips of filaments,meshes, strands or braids of filaments.
 8. Process according to claim 1,wherein, to increase the structural strength of the panel, there isdeposited, by striping or winding, supplemental filaments forming anangle greater than zero with said filaments and disposed on oppositesides or on either side of the porous layer.
 9. Process for theproduction of a panel with a protected acoustic damping layer,comprising the step of: emplacing at least a porous core between a totalacoustic reflector and a porous acoustic damping layer; emplacing saidporous layer by striping or draping in order to obtain parallel stripsdistant one from adjacent ones of said parallel strips; emplacing onlyastride intervals between said parallel strips, strips of a perforatedsheet selected from the group comprising metallic sheets and sheets ofcomposite material constituted of a cloth of fibers pre-impregnated witha thermosetting or a thermoplastic material; and heating saidthermosetting or thermoplastic material in order to ensure thesecurement of edges of said parallel strips with said strips ofperforated sheet.
 10. Process according to claim 9, said perforatedsheet is coated with a thermofusible glue.
 11. Process according toclaim 9, wherein the strips of perforated sheet have a widthsubstantially greater than that of the parallel strips of the porouslayer and are first deposited on the mold with a slight partial overlapbetween strips, then the porous layer is deposited so as particularly toalign each parallel strip with a sheet strip, the windings of saidporous layer not touching each other.
 12. Process according to claim 9,wherein the strips of said perforated sheet have a width less than thatof the parallel strips of the porous layer which is first deposited onthe mold, such that the windings overlap slightly, then the strips ofsaid perforated sheet are placed facing or not the regions of overlap ofthe parallel strips of the porous layer, said parallel strips nottouching each other.
 13. A process according to claim 9, wherein saidstrips of perforated sheet are metallic sheets covered with athermofusible glue.
 14. Process for the production of a panel with aprotected acoustic damping layer comprising the steps of: emplacing atleast a porous core between a total acoustic reflector and a porousacoustic damping layer; emplacing said porous layer by striping ordraping a cloth of filaments pre-impregnated with a thermosetting or athermoplastic material, said cloth being deposited so as to form stripsor windings with a slight mutual overlap; and heating said thermoplasticor thermosetting material in order to ensure the securement of edges ofsaid strips.
 15. Process for the production of a panel with a protectedacoustic damping layer comprising the steps of: emplacing at least aporous core between a total acoustic reflector and a porous acousticdamping layer; striping or draping on a mold said total reflector, thensaid porous core, then, after baking in an autoclave and withdrawal fromthe mold, striping or draping said porous layer in order to obtainparallel strips; striping or draping filaments pre-impregnated with athermosetting or a thermoplastic material; and heating saidthermosetting or thermoplastic material in order to ensure thesecurement of edges of said parallel strips with said filaments.
 16. Aprocess for the production of a panel with a protected acoustic dampinglayer comprising the steps of: emplacing at least a porous core betweena total acoustic reflector and a porous acoustic damping layer, saidstep of emplacing said porous acoustic damping layer comprises inemplacing said porous acoustic damping layer by striping or draping inorder to obtain parallel strips distant one from adjacent ones of saidparallel strips; emplacing only astride intervals between said parallelstrips, strips of a perforated sheet; securing edges of said parallelstrips with said strips of perforated sheet.
 17. A process according toclaim 16, wherein said strips of perforated sheet are metallic sheetscovered with a thermofusible glue.